Given a binary tree, find its maximum depth.The maximum depth is the number of nodes along the longest path from the root node down to the farthest leaf node.

Note: A leaf is a node with no children.

Example:

Given binary tree [3,9,20,null,null,15,7],

3   / \  9  20    /  \   15   7

return its depth = 3.

1 public int maxDepth(TreeNode root) {
   //树 递归 my2         if(null==root){3             return 0;4         }5         int ld=maxDepth(root.left);6         int lr = maxDepth(root.right);7         int d = ld>lr?(ld+1):(lr+1);8         return d;9     }

 

还可以使用BFS

 

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